Contralateral bone conducted sound wave propagation on the skull bones in fresh frozen cadaver

Abstract

The study aimed to investigate the efficient pathway for BC sound transmission by measuring vibrations on the opposite side of the skull bone, referred to as the mastoid position. The realistic contralateral transmission pathway of bone conduction (BC) vibrations is investigated through each osseous structure in the midlines of the fresh-frozen whole head. BC stimulation is applied to the mastoid using a bone vibrator, and acceleration responses are observed on the contralateral mastoid bone and seven midline points of skull bones using triaxial accelerometers. The study finds that the range showing the highest contralateral transmission efficiency of bone vibration is the intermediate frequency range with contralateral direction. Within this range, a significant amplitude of acceleration response is measured at the face-side points and the back and upper parts of the head. The thesis suggests that signal transmission from the specific midline to the mastoid can be more efficient than the conventional configuration of BC from the mastoid to the mastoid.

Figure 1

Measured vibration of cadaver head excited by the bone vibrator at mastoid position (The color and symbol of the curve correspond to the color and symbol of the direction of the arrow in the figure below): (a) autospectrum of the vibration of cadaver head excited by the bone vibrator at mastoid position, (b) frequency response (FR) of the cadaver head at the opposite mastoid positions excited by the bone vibrator at mastoid position.

Figure 2

Autospectrum of the vibration of cadaver head excited by the bone vibrator on the midline. The averaged values of three accelerometers are shown for each direction.

Figure 3

Frequency response (FR) of the cadaver head at the midline positions excited by the bone vibrator at mastoid position, referred to: (a) y-direction at excitation position, (b) z-direction at excitation position, (c) x-direction at excitation position. The averaged values of three accelerometers are shown for each direction.

Figure 4

Standard deviation of the measured autospectrum of the vibration of cadaver head excited by the bone vibrator at mastoid position.

Figure 5

Comparison of the phase responses of cadaver head, referred to function generator output (Red, Acc. No. 2; Green, Acc. No. 3; Blue, Acc. No. 4).

Figure 6

Normalized autospectrum of the vibration of cadaver head excited by the bone vibrator at mastoid position with pure tone signal: (a) 250 Hz, (b) 500 Hz, (c) 1 kHz, (d) 2 kHz.

Figure 7

Coherence between each accelerometer output at the midlines of cadaver head excited by the bone vibrator at mastoid position and: (a) y-direction at mastoid position (Sensor 5), (b) z-direction at mastoid position (Sensor 5), (c) x-direction at mastoid position (Sensor 5).